What's the biggest derby in the world?

[Henrik Larsson]

Since the old firm game is in just over an hour, it made me thing of this.

Mine would be

Celtic vs Rangers
Barcelona vs Real Madrid
Galatasary vs Fenerbahce
Ac Milan vs Inter Milan.
West ham vs Millwall


This link has a good link with good videos showing the atmosphere
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The atmosphere amongst Celtic fans at the full-time whistle shows how important this derby match is.

What would you say is the fiercest derby you know of? The rivalry with the best atmosphere.